1. Field of the Invention
The present invention relates to a photovoltaic element array and a method of fabricating the same and, more particularly, to a photovoltaic element array in which the resistance value of a connecting portion for connecting photovoltaic elements in series is decreased, and a method of fabricating the same.
2. Description of Related Art
An integrated solar battery is known in which a large number of photovoltaic elements are formed on a single substrate and connected in series in order to increase the output voltage of the solar battery. As a method of forming a large number of photovoltaic elements on a single substrate, e.g., U.S. Pat. No. 4,292,092 discloses a technique of dividing a transparent conductive layer and a photoelectric conversion layer formed on a substrate by using a laser, i.e., a laser scribing technique. U.S. Pat. No. 4,697,041 discloses a technique of electrically connecting the upper electrode of a photovoltaic element and the lower electrode of an adjacent photovoltaic element by using a laser.
In addition, e.g., U.S. Pat. No. 4,532,372 discloses a technique of effectively returning light leaking from a semiconductor layer to this semiconductor layer by arranging a transparent conductive layer between a metal layer serving as the lower electrode of a photovoltaic element and the semiconductor layer.
In order not to decrease a light-receiving area in a photovoltaic element array having photovoltaic elements connected in series, a demand arises to minimize the width of an electrical connecting portion between the upper and lower electrodes. This demand however results in an increase in resistance value of the electrical connecting portion and an increase in series resistance of the photovoltaic element array.
In a structure obtained by sequentially stacking an insulating layer of silicon carbide (SiC), a metal layer of aluminum (Al), and a transparent conductive layer of zinc oxide (ZnO) on a metal substrate, a high laser beam intensity is required to form a groove which divides the lower electrode, i.e., the metal layer and the transparent conductive layer because zinc oxide has a high transmittance with respect to a laser beam. The insulating layer is damaged by the laser beam causing short circuits with the metal substrate. Also in a structure obtained by stacking a metal layer and a transparent conductive layer on a substrate of an insulating resin film such as a polyimide film, the resin film substrate may be damaged by the energy of the laser beam.
When aluminum is used for a metal layer and zinc oxide is used for a transparent conductive layer, the transparent conductive layer conducts heat generated by laser irradiation, oxygen in zinc oxide is entrapped by aluminum, and zinc remains. As a result, the light transmittance of the transparent conductive layer is undesirably decreased. Further, when a groove which electrically divides the upper electrode, i.e., a second transparent conductive layer on a light incident side is to be formed by a laser beam, a semiconductor layer (photoelectric conversion layer) formed below the second transparent conductive layer is damaged by heat.
Further, in connecting the upper and lower electrodes using a laser, the semiconductor layer and the upper and/or lower transparent conductive layer may peel off due to the energy of the laser beam.